1. Field of the Invention:
The present invention relates to pressure testing of thin wall cylindrical drums (e.g., 55-gallon drums and the like), wherein multiple drum areas such as the vertical weld seam, top and bottom chines, drum side walls and ends can be simultaneously tested and at high pressures of 10-100 p.s.i.
2. General Background:
A number of thin wall containers, referred to generally as drums, are used for containing various liquid products for shipping. A common drum size which is used for the shipping of oil, chemicals, and the like, is a 55-gallon drum. These drums are usually metallic but can also be of plastic construction. The 55-gallon drum has a relatively small wall thickness of, for example, 14-24 gauge steel. In the construction of these thin-walled drums, a rectangular sheet of metal is first trimmed and shaped to be a "true" rectangle. The rectangle is then formed into a cylinder by welding a vertical seam that connects the two edges of the rectangle. This cylindrical member is then shaped as desired, adding, for example, one or more annular rings which extend outwardly and provide a rolling surface for moving the drum by rolling it. After the cylindrical drum sidewall is shaped as desired, circular drum ends are added, usually by machine.
One of the circular ends defines a bottom end and is a closed end. The other end is the top end of the drum and provides usually a pair of spaced-apart threaded openings, normally a larger opening and a smaller opening. These threaded openings are typically fitted with fittings and closure caps so that liquid can be added to or removed from the drum during its normal use and the drum can then be closed and sealed.
Another type of drum is similar except that one end, usually the top end, is fully removable with the removable end held in place for shipping or storage by a ring that clamps the head and body of the drum firmly together between a gasket seated between a curl on the head and a rounded surface rolled into the body of the drum. This type of construction enables the drum to be emptied under circumstances where it is desirable to have access to the drum through its entire top surface.
The assembly of metal drums as aforedescribed requires inspection of the drums for leakage because of the thin-walled construction of the drum and because of the presence of a number of seams where leakage might occur. Further, the drum wall itself can have small laminations or defects in the metal which could be the source of leakage. Often the leakage occurs after the drum has been filled with fluid, and thus is under increased load and pressure. When the drum is transported, moved, jolted, etc. any weak spots in the drum wall, in the seams and at the joint between the drum ends and the sidewall can fracture or open causing leakage and loss of product.
Because the drum wall and drum ends are relatively thin, pressurizing the drum beyond a few pounds per square inch (p.s.i.) has been avoided by the industry is routine assembly line testing. Typically, drums are tested at about seven (7) p.s.i. as a maximum. By pressurizing the drum to seven (7) p.s.i., an inspection of the drum can be made by manually spraying the drum with a wetting agent, such as soapy water. An inspector then views each of the seams for the presence of any bubbles. This is a time consuming and labor intensive process. Often testing is the weak link in the manufacturing process because it takes several seconds for an inspector to adequately check all of the seams of the drum.
Evans Cooperage, Inc. of Harvey, La. as well as most drum manufacturers employ a horizontal drum tester which holds the ends of the drum during testing using a clamping mechanism. However, testing has always been done at, or about seven (7) p.s.i. In this type of apparatus, the drum is rotated so that the welded seam is easily visable to the operator of the tester then sprayed with a fluid wetting agent, such as soapy water. An observer then visually inspects the drums for bubbles at the vertical seam and a small adjacent area of the horizontal rolled inseam which normally would be in the top and bottom of the drum. This horizontal tester typically only inspects these above-mentioned areas of the drum.
In this existing drum test system in order to improve the test quality, the bottom seam test requires that the drum be removed from the horizontal tester and placed in a separate station which is simply a "pan" of water. This pan of water extends upwardly approximately three to four inches from the bottom end of the drum upwardly along the sidewall of the drum, thus covering the seam between the sidewall of the drum and the drum bottom end. The pan is filled with a wetting agent, such as soapy water, and the drum is pressured internally to seven (7) p.s.i. and visually inspected for leaks. The drum is pressurized with approximately seven (7) p.s.i. air pressure by attaching a fitting supplied with a source of compressed air to the threaded opening at the top of the drum.
This pan test is a manual operation which requires a separate station, separate inspectors, and separate testing equipment. In another supplementary system, if a more accurate test is desired, the drum is pressurized to seven (7) p.s.i. and then mechanically submerged. A leak is indicated on any part of the entire surface by bubbles caused by air escaping from the area that leaks. This is more accurate than the conventional clamping method mentioned above and previously was very time consuming.
To speed up the above process, a multi-station submerged tester previously was developed by Evans. Whereas it was an improvement over previous methods of testing, it was limited to approximately seven (7) p.s.i. and would not totally locate the leak in the drum nor would it produce the shocking effect necessary to locate cold welds or tight lamination.
The testing of drums to seven (7) p.s.i. typically finds some of the obvious leaks in the drum which occur as a defect in manufacture. However, higher pressures would reveal areas which are suspect or weak yet do not readily leak air upon the application of the pressure of seven (7) p.s.i. The problem with using higher pressures for testing purposes is that the increased level of pressure can damage or rupture the drum ends or cause them to bulge. Thus, testing at higher pressures, i.e., above seven (7) p.s.i., has not been used in routine assembly line testing of drums.
If a drum could be tested at higher pressures, such as on the order of fifty (50) p.s.i., the drum could be "shocked" to reveal even very small defects, such as cold welds, defects in wall material such as laminations, and otherwise areas that would not initially show leakage, but which subsequently might open during handling or after filling of the drum. Another drum tester used by a European manufacturer, Van Leer of Holland, and others, employ helium. This is a very expensive machine and it suffers because it is not location specific. One knows there is a leak, but not where the leak is. It is also incapable of operating above 7 p.s.i. and lacks the ability to shock the drum for indicating leaks due to cold welds or tight laminations.
Cold welds can and do occur at times in the welding process due to some malfunction in the welding process or defects in the steel. A cold weld can often be sufficiently strong to go undetected in other types of testing and even when filling only to fail when the filled drum is subjected to subsequent rough handling, vibration in transit, or any one of numerous transportation and handling conditions to which most drums encounter after filling. A resultant leakage therefore is much more costly and potentially dangerous and hazardous than if such leak occurred at time of testing or even filling. A tight lamination or other similar defect in the steel used to produce the drum can similarly go undetected in other forms of testing and produce similar results and problems, as described above.
Another system, the differential pressure measurement system, detects a leak by an elaborate method of measuring pressure drop in the drum if a leak occurs. This system lacks the accuracy of the helium tester. It also suffers from the deficiency of the helium system in that it does not locate the leak nor does not provide for high pressure shocking.
Thus, it is an object of the present invention to provide an improved testing apparatus for the testing of thin wall metal drums and the like wherein the drum can be tested at high pressures, and shocked, (i.e., high pressure plus relatively short time period), in order to reveal even very small leaks which typically do not leak upon the introduction of pressure under ten (10) p.s.i. It is another object of the invention to provide a multiple test drum testing apparatus which simultaneously tests the drum wall, seams (both top and bottom), vertical weld, and at high pressures even up to one hundred fifty (150) p.s.i. without damaging the drum.
There are various patented constructions which relate to the testing of metal drums and the like. Examples of very early patents that relate to testing and containers can be seen in the Maede U.S. Pat. No. 1,547,126, entitled "Vacuum Testing Machine For Empty Cans"; the Wilsdorf U.S. Pat. No. 2,055,568, entitled "Testing Apparatus For Fluid Tight Casings"; and the Troxel U.S. Pat. No. 2,118,906, entitled "Advertising Demonstrator".
An apparatus for testing cans is the subject of the Wimmer U.S. Pat. No. 3,306,097. The Wimmer device uses a circular end plate to support one end portion of the can during testing (see FIG. 1 of the Wimmer '097 patent).
The McCoy U.S. Pat. No. 2,880,610, entitled "Sealing Unit For Drum Testers", shows a typical drum having a plurality of circumferential annular ridges extending away the drum surface. The drum tester uses a cylindrical casing which fits around the outside of the drum.
The Filler U.S. Pat. No. 3,930,401, entitled "Container and Leak-Testing System Therefor", provides a system for testing opening equipped containers for leakage during the entire period, which is usually relatively long, between the time that such containers are fabricated by the manufacturer thereof and the time that they are filled by the user with the product intended therefor. The system includes a testing method, a particular test closure or cap and structural relationship thereof with a container opening, and apparatus for establishing a pressure differential between the interior and exterior of any container under test. In the practice of such system, a pressure differential is established between the interior and exterior of the container, such as by vacuuming the container interior; seating a closure cap of particular character against surfaces of the container in covering relation with the opening thereof, and sealingly relating the closure cap to the container and thereafter maintaining the sealing relationship therebetween using, in each instance, only the pressure differential as the seating and sealing force; transporting the sealed container from its place of fabrication to the place of use, either directly or with intermediate storage periods; band before the container is to be filled with a product, testing the tightness of the closure cap against the container as an index of the presence or loss of the pressure differential.
The Hass et al. U.S. Pat. No. 3,987,664, entitled "Dry-Testing System For Detecting Leaks In Containers", provides a leak detection system capable of efficiently dry-testing containers such as steel drums of large capacity. The system includes a test station constituted by a hermetically-sealed chamber adapted to receive a container to be tested and provided with a retractable head coupled to an external fill assembly. The head functions to sealably engage the bung hole or other container opening and to fill the container with pressurized air, the pressure within the container being maintained during the test period at a constant level, whereby physical distortion of the container is controlled. The pressure within the test chamber is sensed and the output of the sensor is applied to a data processor wherein the influence of temperature on the test chamber pressure is discounted by means of a waveform scanning technique, making it possible to determine the extent to which the container under test is heated and to predict the error pressure in the chamber due to thermal effects. The data processor yields an output signal indicative of the container condition and independent of thermal effects.
U.S. Pat. No. 4,686,850, entitled "Method And Apparatus For Testing Drums", is an earlier of the Applicant herein. In the Evans '850 patent there is provided a method and apparatus for testing drums such as steel drums, wherein the drums are moved automatically into a pre-determined area, and the drums are rotated and oriented, air under pressure is next introduced into the drums, and wherein after an operator observes the drums for leaks, the drums are mechanically lifted from a water filled area. This testing device has not the capability to test beyond about 7 p.s.i, namely, the pressure at which the drum ends bulge or deform.
The McDaniel U.S. Pat. No. 4,747,298, entitled "Container Leak Detector", provides a container testing apparatus and method for detecting leaks in containers such as at the rims of the container. Preferred apparatus have opposing testing heads with receptacles for receiving ends of a container. Each testing head has two seals. A first or end seal is preferably adapted to seal at the end wall of the container. The second or perimetric seal is expandable against the sidewall of the container. The perimetric seal has an internal expansion chamber which is pressurized to expand the seal into sealing engagement with the container. A differentially pressurized testing fluid is transmitting to a chamber formed between the seals and the container. A detector selectively senses changes in the container associated with the existence of a leak through which the differential pressure of the testing fluid is communicated.